STUDYING THE EBB AND FLOW OF STOP-AND-GO; LOS ALAMOS LAB USING COLD WAR TOOLS TO
SCRUTINIZE TRAFFIC PATTERNS

LOS ALAMOS, N.M. -- Atop a remote mountain rising from the desert floor, scientists who
once wrestled with the fundamental nature of matter and the limits of artificial
intelligence are now trying to unravel an even more daunting mystery:

Why is traffic so damn bad?

Los Alamos National Laboratory, better known as the birthplace of the atom bomb and
home of the world's fastest supercomputer, has turned the covert tools of the Cold War to
the hot-under-the-collar war waged by commuters.

Nuclear physicists who once spoke of "weapons platforms" now talk of
"road rage." Computer models designed to perfect tactics for tank battles are
being retrofitted to forecast highway congestion. And supercomputers developed to test
warheads could simulate the travel behavior of every person between Washington and Boston.

The research in New Mexico is the latest chapter in the romance between traffic and
physics, a relationship that has lured some of the century's sharpest minds to apply
natural laws to the flow of cars along a highway. Physical Review Letters, a premier
scientific journal, averages one article on the topic each month.

These scholars, moreover, are employing their theories where rubber meets the road:
suggesting concrete solutions, from ramp metering lights for ironing out highway traffic
to simulations that can forecast the benefits of specific road improvements.

Through the eyes of a scientist, motorists trapped in a seemingly inexplicable Capital
Beltway backup are actually prisoners of rules that are obscure from behind the steering
wheel. The patterns can be analyzed and, perhaps before long, even accurately predicted.

Yet despite some tantalizing progress, reaching a full understanding of traffic jams
has been slow going. Scientists said they are closer to comprehending the birth of the
universe than the daily tie-ups along Interstate 66.

"Physics offers a wide variety of methods for understanding traffic. But there are
still a lot of open problems," said German physicist Kai Nagel, a key figure in the
Los Alamos project.

Hani S. Mahmassani, a University of Texas professor and perhaps the leading American
expert in traffic flow theory, put it this way: "All of a sudden to go from free flow
to stop-and-go, this remains one of the mysteries of our time."

Traffic Chaos Theories

Some scholars have compared the traffic stream to a fluid, focusing on the waves that
ripple through it as cars brake or accelerate in succession.

Others have tried to explain it in terms of what is known as chaos theory. They suggest
that at certain moments, when a highway is becoming crowded, the flow of cars is so
unstable that a major tie-up can arise from something as minor as a single driver riding
the brakes a split second too long.

One approach likens sudden slowdowns to phase changes, which happen in nature, for
instance, when steam turns to water or water to ice.

In light traffic, motorists drive as they like. As the road grows crowded, drivers
suddenly find themselves being carried along in the traffic stream, moving at a common
speed and often unable to change lanes. This intermediate phase, called
"synchronized" flow, is much like liquid. When traffic goes through a second
transition into stop-and-go, cars are like water particles crystallized into ice.

But although a motorist may be akin to a water particle, a driver trapped at the
Woodrow Wilson Bridge during rush hour is no run-of-the-mill molecule. People adjust their
routes based on yesterday's backups or today's traffic forecasts. Molecules, moreover,
exist to collide into each other. For motorists, that's not so wise.

So although physicists often are drawn to traffic because they recognize similarities
with their traditional work, it is the human element that makes it so intoxicating.

Chris L. Barrett, the scientist who convinced Los Alamos that traffic was a matter of
grave national security and now heads its transportation project, said: "Traffic is
particles with motive. I think it's cool as hell."

The Father of Road Physics

The paternity of traffic science is widely attributed to Robert Herman, known as the
father of the Big Bang because he accurately predicted the microwave echoes of the
creation of the universe long before they were detected.

When Herman initially considered shifting his gaze from the early cosmos to traffic,
his colleagues counseled against it, saying it was too complex.

Undaunted, he joined General Motors Research Labs outside Detroit in 1956. Adequate
scientific equipment was scarce, so Herman and his colleagues followed each other home
from work to observe their own driving behavior.

By the early 1960s, Herman hooked up with Ilya Prigogine, whose Nobel Prize-winning
theories had earned him the nickname the "poet of thermodynamics." They began to
examine traffic as a collective flow.

Where daily commuters see only frustration, late charges at day-care and excuses for
the boss, Prigogine spies a basic organizing principle of the universe. He has likened
traffic to "the magnificently coordinated flight of a large flow of birds or the
remarkable darting collective motion of a school of fish."

In the last 10 years, a new wave of physicists emerged in Germany, home to the leading
think tank at DaimlerChrysler and a ready-made laboratory called the autobahn.

These scholars included the likes of Boris S. Kerner, who found that the change from
free to synchronized flow can happen almost spontaneously -- much faster than scientists
previously thought. Often, it happens near on-ramps, when a sudden burst in the number of
cars entering the road can cause traffic to jell into a single, moving whole. This
sluggish condition will spread up and down the road, persisting perhaps several hours,
long after the ramp has cleared.

In Duisberg, Germany, physicist Michael Schreckenberg made a name for himself as the
"Jam Professor" in part through his real-life experiments. He and about 15
colleagues bundle into a phalanx of five vehicles, set out on the nearby roads and
intentionally create bottlenecks. "It is quite interesting to see how people
react," he said.

Nagel, one of Schreckenberg's main collaborators, was a mere graduate student when he
started making his mark. Now 33, Nagel looks the part of a German intellectual: A curtain
of blond bangs dangle above narrow, oblong black eyeglasses; a green turtleneck peeks
above the collar of a gray sport jacket. Even before he finished his doctorate in physics,
he had refined a process for running simulations faster than ever before and then began
using it to model weather patterns.

But Barrett, at Los Alamos, had other plans in store for him. Barrett needed someone
who could design simulations fast enough to be practical. Nagel became the bridge that
crossed the Atlantic.

Studying for a Solution

Holed up atop their desert mesa, where the biggest backup is two dozen cars idling at a
red light on the serpentine, cliff-side road and rush hour lasts only half an hour,
Barrett's band of physicists, chemists, mathematicians and computer theorists aims to
revolutionize traffic forecasting and planning.

They tapped the lab's Cold War experience in supercomputing and war-fighting models.
Expertise in simulating military logistics and tank battles became the basis for traffic
modeling: "Rip off the turrets and you have cars," quipped one researcher.
Studies of wind currents during so-called nuclear winter laid the groundwork for forecasts
of auto emissions.

After Barrett joined the top-secret Los Alamos weapons lab in 1988, he did something he
can't talk about. That reticence is out of character for so fast-talking a character,
whose roller-coaster soliloquies cascade from idea to idea, physics to biology to moral
philosophy and back, who shuttles as easily between discussions of neural networks and bus
networks as between neckties and bolo ties.

Lately, he's had his ear tuned to traffic.

"Traffic is like music," Barrett said with childlike exuberance.
"Traffic constructs itself like a singer sings. It's the same song. But everyday, the
song is a little bit different."

To capture the countless decisions that individual travelers make in shaping a
metropolitan area's traffic patterns, Barrett's team is creating a vast, mirror world in
cyberspace of every motorist and transit rider, every traffic light, turn lane and bus
stop.

They do this by simulating a region's population, mining census data and other
statistics to create a mirror people with the same ages, incomes, jobs, children.

This virtual population is turned out onto the cyber roads, trains and buses of a
region modeled right down to the duration of red lights and the frequency of buses. The
individuals can adjust their travel habits if the trips take too long, switching to
different streets or from car to bus -- or even finding a new dentist.

The artificial network, still under development, could potentially gauge the precise
benefits of widening a highway, erecting a bridge or building a subway line. It could
measure the effects of changes in car-pool restrictions or cheaper bus fares or even new
technology, such as electric cars. It could forecast the traffic impact of proposed
subdivisions and the graying of a region's population.

The current locale being modeled is Portland, Ore. Washington could be next.

When President Clinton toured Los Alamos last year, he was so impressed by the traffic
model -- and so depressed by this region's gridlock -- that he suggested while returning
on Air Force One that the capital area be modeled. Since then, federal and regional
officials have been briefed but no decision has been made. The program is designed to run
on computers available to local planners and the cost would be about $13 million.

In Germany, Inroads

The theoretical breakthroughs in Germany have their own practical potential. Kerner's
findings about ramp traffic can be used to program metering lights to feed vehicles onto
the highway in a slow and regular fashion. This understanding also could smooth out
traffic by calibrating speed limits to different traffic conditions.

DaimlerChrysler also is developing guidance and navigation systems for Mercedes that
could tap traffic information from a computer network of road sensors that would improve
the driving of individual cars, ironing out disruptions that can cause a sudden slowdown.

In the fall, Schreckenberg plans to launch a project to provide one-hour traffic
forecasts in the Rhine-Ruhr region, comparable to the Los Angeles area, by combining data
from sensors in the road with computer simulation.

This could prove the most significant advance in traffic forecasting during the last 40
years of commuting and computing. But it pales next to what Los Alamos envisions down the
road.

William "Buck" Thompson, a deputy director at Los Alamos and a physicist and
nuclear engineer by training, predicts planners will soon want to construct a model of
every traveler, every car and every street in the megalopolis sprawling between Washington
and Boston. That would require the might of Blue Mountain.

Locked behind heavy blue security doors in the heart of America's most sensitive
weapons lab, Blue Mountain is the pinnacle of computing, actually 6,200 processors in 550
blue and gray computer cabinets, each rising six feet high and arrayed in 14 rows like a
bountiful metallic cornfield.

It is a supercomputer so fast it can process in one second the entire contents of the
Library of Congress, albeit it is a simple task compared to simulating rush hour.

"At some point," Thompson said, "we could be able to model the entire
United States with a machine like this."

Traffic Patterns

Scientists have identified "phase changes" in traffic, similar to the sudden
transitions that occur when steam turns to water or water to ice. Understanding the timing
and dynamics of phase changes in traffic, like those in nature, poses a challenge for
physicists. But this could hold the key to easing the frustration of commuters, including
those traveling along the Outer Loop of the Capital Beltway near the Persimmon Tree Road
overpass in Montgomery County on a typical Tuesday morning.

Phase 1

When traffic is light, motorists drive much as they like, moving at the speed they want
and changing lanes easily. Motorists are comparable to steam particles with great freedom
of movement.

Phase 2

As the road becomes crowded, motorists suddenly lose much of their freedom and are
forced to drive as part of the overall traffic stream, moving at the speed of the general
flow and often unable to change lanes. This phase, similar to water, has been called
"synchronized" flow.

Phase 3

In heavy congestion, traffic is stop-and-go. Like water freezing into ice, the
motorists are stuck in place.